Air circuit breaker (ACB) preventive maintenance

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 Introduction

Air circuit breaker is very important component in power system to protect electrical equipment's from over load, earth fault and short circuit protection. ACB required proper maintenance for optimal performance and long service life and also prevent unexpected and costly failures. In this breaker air is used as the arc extinguishing medium. It is used in widely range in low voltage electrical power system and industrial sectors for its reliability, optimal performance and safety features.

Why ACB preventive maintenance is important?

For save and prevent unexpected and costly breakdowns it is very important to do preventive maintenance of equipment. If preventive maintenance will ignored it can lead to damaged the equipment, fire hazard and totally system failure. Preventive maintenance is very essential to improved system reliability, prevent unexpected and costly failures and downtime, for longer equipment service life, improved safety for personnel and equipment.

Step by step preventive maintenance procedure.

First isolate ACB from main power supply and follow LOTO procedure (lockout/tagout). And then discharge completely storage energy in ACB breaker.

1-Visual inspection

  • First must be inspected sign of wear, corrosion or damaged.
  • Must be inspected the insulation to check for cracks.
  • Must be inspected fixed terminals. 

2- Cleaning 

  • Removed dust, dirt from ACB using soft brush or dry compressed air.
  • Do not use wet cleaning method unless recommended by the manufacturer.

3- Mechanical checks

  • It should be manually operate the ACB for ensure smooth functioning of open/close.
  • As per manufacturer recommendation lubricate the moving parts like trip mechanism, springs.
  • Must be checked for loose bolts.

4-Contact inspection

  • It should be checked the main and arcing contacts for sign of corrosion or pitting.
  • Must be checked contacts alignment.
  • Must be checked arc chute for wear and carbon deposits. Replace arc chute when needed to ensure proper arc extinction.     
  • Must be measured contact resistance with micro ohm meter. If the resistance value is exceed the allowable limit it can indicate overheating and reduce performance.  

5- Insulation resistance testing

  • In this test IR test is performed between phases and phase to earth.
  • If the values below the recommended threshold it can lead potential insulation degradation.
  • In this test apply the test voltage normally 500v to 1000v DC between each phase to phase and phase to earth with ACB close contacts.
  • If the humidity is high it may impact the insulation resistance reading so it is very important to consider humidity factor.


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